The present invention relates to an x-ray diffractometer, spectrometer, or other x-ray analysis application. More specifically the present invention relates to an improved method of generating and measuring the diffraction, spectrometry, or other x-ray pattern for a sample.
A common method used to study crystal structures is x-ray diffraction. The method is based on illuminating a sample crystal with a beam of x-rays. A portion of the x-ray beam is not able to travel directly through the sample crystal, rather some rays are deflected or diffracted and emerge from the sample at varying angles. The incident x-rays make their way along the spaces between the atoms of the crystal or are deflected by the atoms. A sensor is used which detects the x-ray diffraction pattern generated by the x-rays as they emerge from the sample crystal. This diffraction pattern corresponds to the atomic structural arrangement of the crystal. Such a system is known in the art as an x-ray diffractometer.
Traditionally one changes the resolution and the angular range of a diffractometer by adjusting the distance between the sample and the detector. The detector has always been the moving part in previous designs with the sample mounted in a fixed position with respect to the x-ray source. A collimated beam is often used so that the beam spot on the detector will not change significantly while the sample-detector distance is changed. This collimated beam for certain applications does not contain enough flux to generate a readable diffraction pattern.
A focused x-ray beam can be used to obtain higher flux densities upon the sample than is possible with a collimated beam. When generating a diffraction pattern of a sample, the focused x-ray beam is normally directed through the sample and focused on to the detector to obtain the best resolution. The focusing optics traditionally used are bent total reflection mirrors. When the sample-detector distance is changed, the focal length of the mirrors is readjusted to place the focal point on the detector by bending the mirrors. The size and intensity of the focal spot can be adjusted by bending the mirrors. This bending process is a time consuming and relatively inefficient task.
The reflective surfaces in the present invention are configured as multilayer or graded-d multilayer Bragg x-ray reflective surfaces. Bragg structures only reflect x-ray radiation when Bragg's equation is satisfied : EQU n.lambda.=2d sin(.theta.)
where
______________________________________ n = the order of reflection = wavelength of the incident radiation d = layer-set spacing of a Bragg structure or the lattice spacing of a crystal .theta. = angle of incidence ______________________________________
Multilayer or graded-d multilayer Bragg mirrors are optics with a fixed focal point which utilize their inherent Bragg structure to reflect narrow band or monochromatic x-ray radiation. The bandwidth of the reflected x-ray radiation can be customized by manipulating the optical and multilayer parameters. The d-spacing of the multilayer mirror can be tailored through lateral grading in such a way that the Bragg condition is satisfied at every point on the multilayer mirror. The d-spacing may also be changed depthwise to control the bandpass of the multilayer mirror. The d-spacing depth may vary as a function of depth or the d-spacing may be held constant for each layer.
Multilayer mirrors have the ability to increase the flux by more than one order of magnitude with a fine focus x-ray tube, as compared with total reflection mirrors. Multilayer mirrors, because of their monochromatic output, could also reduce any unwanted spectrum. For example, in certain applications the K.beta. radiation emitted from a source and transmitted through a sample could be reduced by thousands of times. With fixed focal point multilayer optics, the traditional resolution adjustment scheme is not suitable because any bending of a multilayer optic will impair the reflective aspects of their Bragg structure. The present invention includes a new technique, which takes advantage of the large amount of narrow bandpass or monochromatic flux generated by multilayer or graded-d multilayer mirrors and maintains the flexibility of changing the resolution and angular range of a diffraction pattern.
The procedure utilized in the present invention involves moving the sample coaxially and rotationally relative to x-ray beam reflective optics during x-ray diffraction analysis. The x-ray reflective optics are static while the sample is maneuvered through varying intensities of the focused x-ray beam, eliminating the need for optics with variable focal lengths. The movement of the sample through the focused x-ray beam will change the resolution, angular range, and intensity of the sample diffraction pattern. This method will allow a more efficient use of multilayer or graded-d multilayer mirrors as opposed to current technology such as total reflection mirror technology. The focal length of the multilayer optics used will be a constant, removing the time consuming task of adjusting focal lengths for total reflection mirrors.
The movement of the sample does not prohibit the movement of the detector. The detector may also be moved in certain applications with or without movement of the sample. In small sample applications where a sample is placed directly upon the focal point of a focusing optic, movement of the detector may be desired.